In so-called high-voltage MOS transistors, there is a tendency that heavy concentration of electric field takes place in the vicinity of drain edge of the channel region, and thus, the breakdown voltage at the drain edge is an important issue. Such a high-voltage MOS transistor may be used in various applications such as in-vehicle applications, power applications, and the like.
It is preferable to integrate such a high-voltage MOS transistor in the form of an integrated circuit together with logic circuits, and the like. On the other hand, when such a high-voltage MOS transistor is integrated with logic circuits, the gate insulation film is formed to have a small thickness similarly to the transistors of logic circuits. Thus, in such a high-voltage MOS transistor, there is used a construction in which the drain region is formed with large separation from the gate electrode such that there is formed a drift region between the gate electrode and the drain region for improving the breakdown voltage in the vicinity of the drain edge. For example, there is a so-called LDMOS (Laterally Diffused MOS) structure. For example, reference should be made to Patent Reference 1 or 2.